This invention relates to a silica in which a part of silicon is chemically bonded to hydrogen, and more particularly, to a novel finely divided silica derivative which has a Si--H bond utilizable in chemically useful reactions such as reduction reaction, hydrosilylation reaction and the like and which is in the solid form that is convenient in industrial use, particularly the spherical form and has a uniform particle size distribution, and to a process for producing the same.
Solid, amorphous silicon dioxide represented by the general formula SiO.sub.2 and generically named silica is used in a large amount as silica glass, or a moisture absorbent (silica gel), also as a catalyst carrier or the like because it is chemically inactive and resistant to high temperatures, and further as a filler for silicone rubber or the like. In particular, fine particles thereof are widely used in industry as a filler for rubber called white carbon, a thickening agent for liquid, or an anti-caking agent for powders, and further as a spacer for liquid crystal display though it is a special example, or the like.
Among them, in such uses as filler for rubber and the like, there is used inexpensive, finely divided silica which is produced by a method which comprises neutralizing sodium silicate with an acid such as sulfuric acid or the like, and in uses requiring a high quality, there is used finely divided silica having a uniform particle size distribution obtained by a method which comprises hydrolyzing tetraethoxysilane with a mixture of water and ammonia using an alcohol as a reaction solvent, as disclosed in, for example, JP-A-62-52119.
However, as stated above, most of the prior art methods of utilizing silica have been physical applications such as a catalyst carrier, a moisture absorbent, a filler for resin and the like, which applications utilize solely physical characteristics of silica such as viscosity, strength and hardness.
It has not been deeply studied to impart chemical characteristics to silica per se and utilize the same; however, there has been made such a device as to apply various chemical modifications to the silica surface depending upon the purposes. There have been proposed such methods as a method which comprises adding a compound having a double bond to the OH group present on the silica surface to make the silica excellent in compatibility with a resin, a method which comprises incorporating a finely divided silicon hydride represented by the general formula SiH.sub.x into a coating agent to impart a rust-preventiveness to the coating agent because the silicon hydride has an excellent rust-preventing effect based on the reducibility of hydrogen (JP-A-56-145,111), and the like.
Silicon hydride is an effective means for allowing silica per se to have chemical characteristics and using the same. However, silicon hydride must be prepared by using a monosilane gas or its chloride, which is expensive and, in addition, instable and difficult to handle as the starting material and subjecting the same to gaseous phase pyrolysis reaction. Therefore, the silicon hydride is high in production cost and, in addition, chemically instable and high in combustibility and hence difficult to handle. Thus, it is unsuitable for general utilization.
Silica is generally produced by a method comprising subjecting to hydrolysis-condensation a hydrolyzable silane such as a tetraalkoxysilane; an alkylalkoxysilane obtained by alkylating a part of the alkoxy groups of the tetraalkoxysilane; or the like. However, the hydrolysis-condensation reaction of these hydrolyzable silanes is slow, and hence, severe reaction conditions using a basic catalyst must be adopted for producing silica. Therefore, it is very difficult to obtain silica having a reactive group such as Si--H, which is easily converted to an inactive hydroxyl group as a side reaction.